X-ray counting system
DM0011
1
SENS-TECH
SENSOR TECHNOLOGIES
description
The DM0011 is a wide dynamic range, X-ray counting system.
X-rays up to 100 keV are detected using a scintillator coupled to
a photomultiplier and signal processing electronics to provide a
TTL output.
The detector uses a window discriminator to detect X-rays
within a selected energy band. The width and threshold (lower
limit) of the window and the HV of the photomultiplier can be set
by the user with the DM0011CONTROL. A schematic of the
window discriminator and read out is shown in section 5.
Fast count rates are achieved by using a YAP(Ce) scintillator,
selected for its very fast (30 ns) decay time, and high speed
electronics, designed to minimise dead-time. A plot of indicated
counts against true counts is shown in section 6.
As well as counting X-rays in a set energy band, the unit can be
used to generate an energy spectrum by using a narrow
(energy) window and progressively increasing the lower
threshold. This feature is also used to calibrate the detector,
using gamma and X-ray sources of known energy. A sample
energy spectrum is shown in section 7.
5
window discriminator schematic
Only pulses falling in the window, between the lower level
(LLD) and upper level (ULD) are detected.
2 applications
The unit is designed to count X-rays in laboratory or production
equipment and in synchrotron radiation experiments.
shaping
amplifier
YAP(Ce)
logic and
O/P driver
ULD
pmt
X-ray
3 features
+HV
+HV
·
10 MHz count capability
·
0.15 Hz background count
·
adjustable window discriminator
·
adjustable sensitivity
·
compact assembly
·
operates from a single low voltage supply
·
TTL output
0.100 V
3.00 V
variable, 3 V max
10 MHz max (note 1)
5 MHz max
YAP (Ce) 21.8 mm dia
0.15 Hz (note 2)
+4.75 V min
+5.25 V max
ripple < 100 mV pk-pk
60 mA max at 1 MHz
count rate
note 1: after dead-time correction
note 2: 0.15 Hz maximum (8 keV to 50 keV), unit shielded with 6 mm of lead
signal > ULD
0V
output
37 ns
indicated counts vs true counts
The true count rate N can be calculated from the measured
-Nt
value n by iteration, using the expression n = Ne , where t
is the
dead-time. This may be approximated for nt
<<1 to
N = n/(1-nt
).
n MHz
supply current
5 keV to 100 keV
signal < LLD LLD < signal
< ULD
LLD
6
4 specification
detection range
window discriminator
lower (min)
upper (max)
window width
count rate
actual counts
indicated counts
scintillator
background counts
supply voltage
ULD
LLD
10
9
8
7
6
5
4
3
2
1
0
0
1
2
n
3
4
5
6
N MHz
linear response
7
8
9
10
n = Nexp(-Nt
)
9
outline drawing (mm)
35.0 dia
The detector is calibrated using very low activitity sources; for
55
241
example, Fe (5.9 keV), Am (17.0 keV and 59.5 keV). The
discriminator window is set, using the DM0011 CONTROL, to
the lowest width of 50 mV. The lower threshold of the window is
raised in steps, from a minimum of 50 mV up to a maximum of
3 V. The counts are recorded at each step and plotted against
the voltage of the window centre (= threshold voltage plus half
the window width). The voltage of the window centre has a
linear relationship to the mean energy of the detected X-rays,
enabling an energy spectrum to be produced, as illustrated in
the figure below.
21.8 active dia
±0.25
±0.25
±0.25
31.00
29.00
62.0
calibration and generation of energy
spectra
7
DM0011 data sheet
page 2
'C'
'A’
'B'
800
600
200
connectors
5.9 keV
0
200
400
600
800 1000
window centre mV
1200
55
Fe
1400
‘A’ -
TTL signal out
BNC
‘B’ -
power input
Lemo EGG.00.302.CLL
pin 1 +5 V
pin 2 0 V
‘C’ -
control unit interface
241
Am
The coordinates of the three peak positions are transferred to
a linear calibration curve relating X-ray energy to mV setting,
as shown. Alternatively, the scale on the x axis in the above
graph may be expressed in keV by using the calibration
curve. The detector can then be used to generate the
absolute energy spectrum of an unknown X-ray source by
using the some procedure as for calibration.
scintillation crystal
photomultiplier
type 9107SB08
±0.5
59.5 keV
400
0
alternative connector
positions for DM0011-01
shown dotted
80.0
count Hz
17.0 keV
pin 1, signified by red dot
on rim of aperture
'A'
energy, keV
±0.25
60
'B'
50
80.00
70
40
30
'C'
20
10
0
0
200
400
600
800
window centre mV
1000
1200
standard
connector
positions
for DM0011
±0.25
118.00
10 precautions
Avoid touching the scintillation crystal window. It is a very thin
membrane and, consequently, is very delicate.
Sens-Tech Limited
6A Langley Business Centre,
Station Road, Langley
Berkshire, SL3 8DS, UK
tel:
+44 (0)1753 214714
fax:
+44 (0)1753 214715
e-mail: [email protected]
The company reserves the right to modify these designs and
specifications without notice. Developmental devices are intended for
evaluation and no obligation is assumed for future manufacture.
While every effort is made to ensure accuracy of published information
the company cannot be held responsible for errors or consequences
arising therefrom.
an ISO 9001 registered company
www.sens-tech.com
SENS-TECH
SENSOR TECHNOLOGIES
© Sens-Tech Limited, 2007
DS_ DM0011 issue 1
30 march 2007